class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        if( head==null )
            return head;
        ListNode cur = head;
        while( cur.next!=null ){
            if( cur.val==cur.next.val ){
                cur.next = cur.next.next;
            }else{
                cur = cur.next;
            }
        }
        return head;
    }
}